Continuing development of internal combustion engines and the desire for increased intervals between oil changes places ever increasing demands on lubricating oils. Two properties in particular for which improved performance is desired are dispersancy and oxidation resistance. Typically the approach to improving such properties involves developing specific performance additives which are blended with an appropriate base oil.
Research Disclosure 13449 of June 1975 discloses the use of aromatic sulfonyl azides containing a carboxylic acid (or anhydride) group in the preparation of functionally substituted EPM and EPDM polymers. The sulfonyl azides are said to decompose thermally to give sulfonyl nitrenes which become grafted to the EPDM polymers by addition across carbon-carbon double bonds (giving aziridines) and insertion into C-H bonds. Thermoplastic ionomers with attractive physical properties are obtained by compounding the engrafted EPDM polymers with metal salts.
U.S. Pat. No. 3,220,985 (filed Oct. 15, 1962) discloses modification of polymers including Cis-1,4-polyisoprene, polybutadiene and styrene-butadiene rubber, particularly polypropylene and polyisobutylene, by heating with a monosulfonyl azide having the formula RSO.sub.2 N.sub.3 wherein R represents an organic radical (e.g. 3-azidosulfonylbenzoic acid), in order to prepare products having improved dyeability, emulsifiability and adhesion to other materials. UK Patent 1,446,062 discloses modification of similar polymers with mixed anhydrides of sulfonylazides with at least one carboxyl group.
U.S. Pat. No. 4,440,659 (filed Feb. 19, 1982) discloses the preparation of ashless dispersants suitable for adding to lubricating oil by co-grafting maleic anhydride and an alkyl acrylate or methacrylate onto a Bright Stock mineral oil backbone followed by reaction with an amine to form amides and/or imides.
It has now surprisingly been found possible to modify directly a base oil by molecular attachment of certain aromatic groups via a sulfonamido linkage and thereby achieve enhanced dispersancy.